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Appendix //.

P. J7J-. Intensifying Compressor.—The differential hy-
draulic principle shewn in Fig. 727, p. 737, is a convenient means
of obtaining high pressure with small load, if little quantity of water
be desired, or a double-acting apparatus be permissible for con-
tinuing the stroke. It may equally well be applied to testing
machines for intensifying town's water, and is so shewn in Fig.
804, which represents Messrs. J. Stone & Co.'s apparatus for


testing pipe mains. The town's water is admitted through cock
A, and acts at B on the larger area, thus intensifying the water
in c, where the load is received on the annulus. The pressure
water then passes along pipe D to the main E being tested, and
the pressure is shewn at F. The cock A is so arranged that
town's water may be first admitted into c, D, and E, after which
the flow is diverted to B and intensification takes place, the ram
rising till its stroke is complete. If the test be not then finished,
cock G is closed, while c and B are placed in equilibrium by means
of cock A, and the ram is once more lowered. Again closing A,
the pressure is intensified instantaneously in c, and G being
opened, the test continues.

In a double-acting apparatus made by the same firm, a pair
of rams are used, one being up while the other is down, and the
cock, A, one to each ram, is opened and closed automatically by